This invention relates generally to polymer polyol formation and, more particularly, to a process for preparing a transesterification stable preformed stabilizer for use in the formation of polymer polyols.
Polymer polyols, also know as graft polyols, are well know in polyurethane chemistry. They find special use in the formation of certain foams with special properties. Typically, graft polyols are formed as the reaction product of ethylenically unsaturated monomers with a macromer in the presence of a carrier polyol, a reaction moderator, optionally a preformed stabilizer, and a free radical polymerization initiator wherein the monomers copolymerize with the macromer. One of the difficulties associated with current processes for preparing graft polyols is that the reactors tend to accumulate fouling, which is a particularly significant problem for continuous reactors. This fouling causes the reactors to quickly become plugged with sediment of unstable compounds in the reaction. The reactor must be shut down and cleaned, leading to a loss in productivity of the reactor. Thus, it would be highly advantageous to create a process for the formation of graft polyols having a reduced tendency for fouling.
The typical macromers are polyether polyols having induced unsaturation prepared by reacting any conventional polyol with an organic compound having both ethylenic unsaturation and a carboxyl, anhydride, isocyanate, epoxy, or other group reactive with an active hydrogen-containing group. Suitable unsaturated isocyanates include compounds such as isocyanatoethylmethacrylate (IEM) and 1,1-dimethyl meta-isopropenyl benzyl isocyanate (TMI). Macromers are usually prepared in the presence of a Lewis acid catalyst.
The preformed stabilizers of the present invention, which are also graft polyols, are prepared by reaction of ethylenically unsaturated monomers with the macromer in the presence of a carrier polyol, a reaction moderator, and a free radical polymerization initiator. One problem associated with this reaction is the tendency to have formation of transesterification products between the macromer and the carrier polyol wherein the unsaturated group on the macromer gets transferred to the carrier polyol. This transesterification product can then cause problems in the subsequent graft polyol formation reaction using the preformed stabilizer. Thus, it would be advantageous to develop a method for reducing the transesterification reaction during formation of the preformed stabilizer or final graft polyol product.